Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for handling radio access network (RAN) assistance information for radio link failure (RLF) in a wireless communication system.
Related Art
3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
3GPP/wireless local area network (WLAN) interworking has been discussed. 3GPP/WLAN interworking may be called traffic steering. From rel-8 of 3GPP LTE, access network discovery and selection functions (ANDSF) for detecting and selecting accessible access networks have been standardized while interworking with non-3GPP access (e.g., WLAN) is introduced. The ANDSF may carry detection information of access networks accessible in location of a user equipment (UE) (e.g., WLAN, WiMAX location information, etc), inter-system mobility policies (ISMP) which is able to reflect operator's policies, and inter-system routing policy (ISRP). Based on the information described above, the UE may determine which Internet protocol (IP) traffic is transmitted through which access network. The ISMP may include network selection rules for the UE to select one active access network connection (e.g., WLAN or 3GPP). The ISRP may include network selection rules for the UE to select one or more potential active access network connection (e.g., both WLAN and 3GPP). The ISRP may include multiple access connectivity (MAPCON), IP flow mobility (IFOM) and non-seamless WLAN offloading. Open mobile alliance (OMA) device management (DM) may be used for dynamic provision between the ANDSF and the UE.
The MAPCON is a standardization of a technology which enables configuring and maintaining multiple packet data network (PDN) connectivity simultaneously through 3GPP access and non-3GPP access, and enables a seamless traffic offloading in units of all active PDN connections. For this, an ANDSF server provides access point name (APN) information for performing offloading, routing rule, time of day information, and validity area information, etc.
The IFOM supports mobility in a unit of IP flow, which is more flexible and more segmented than the MAPCON, and seamless offloading. The IFOM enables access to different access networks even when the UE is connected to a PDN using the same APN, which is different from the MAPCON. The IFOM also enables mobility in a unit of specific IP traffic flow, not a unit of PDN, for a unit of mobility or offloading, and accordingly, services may be provided flexibly. For this, an ANDSF server provides IP flow information for performing offloading, routing rule, time of day information, and validity area information, etc.
The non-seamless WLAN offloading is a technology that offloads traffics completely so as not to go through the evolved packet core (EPC) as well as that changes a path of a specific IP traffic to WLAN. The offloaded IP traffic cannot be moved to 3GPP access seamlessly again since anchoring is not performed to the P-GW for mobility support. For this, an ANDSF server provides information as similar as the information provided for the IFOM.
For efficient traffic steering between 3GPP/WLAN, radio access network (RAN) assistance information may be provided by the network. During radio link failure (RLF), how to handle the RAN assistance information may need to be defined.